The present invention relates to an optical switch based on a rotating vertical micro-mirror positioned off-set from its axis of rotation, and in particular, to a method and apparatus for using a MEMS-based device to steer and manipulate beams of light traveling in free-space in an optical switch.
Fiber optics technology is revolutionizing the telecommunications field. Optical switches can be used to turn the light output of an optical fiber on or off, or, alternatively, to redirect the light to various different fibers, all under electronic control. Such switches can be used in a variety of different applications, including, for example, devices such as add-drop multiplexers in wavelength-division-multiplexing systems, reconfigurable networks, hot backups to vulnerable components, and the like. In those and other applications, it would be useful to have optical switches characterized by moderate speed, low insertion loss, high contrast ratio and low manufacturing cost.
Known optical switches may be categorized generally as belonging to one of two classes. One class may be referred to as bulk opto-mechanical switches. In such switches, an input fiber, typically engaged to a lens, is physically translatable from a first position to at least a second position. In each position, the input fiber optically connects with a different output fiber. Bulk opto-mechanical switches possess several desirable characteristics, including low cost, low insertion loss, low back-reflection, and insensitivity to polarization. Unfortunately, such opto-mechanical switches are slow, having response times within the range of 0.1 to 10 seconds.
A second type of optical switch may be referred to as an integrated-optical switch. In such switches, an input fiber is coupled to a planar waveguide, typically lithium niobate or silicon. Output fibers are connected to various output ports of the waveguide. The electro-optic effect, whereby application of a voltage to the waveguide changes the refractive index of the various regions of the waveguide, is used to change the route of an optical signal traveling through the planar waveguide. In this manner, an input signal can be switched to one of a variety of output fibers. While such switches are very fast, they are quite expensive and frequently polarization sensitive.
As such, there is a need for a low cost optical switch possessing the desirable characteristics of opto-mechanical switches, but having a much greater switching speed.
The present invention is directed to a MEMS-based device that steers and manipulates beams of light traveling in free-space in an optical switch.
The optical switch is based on one or more rotating vertical micro-mirrors constructed on a surface of a substrate. At least one input optical fiber is arranged to direct at least one optical signal through free-space generally over the surface of the substrate. A plurality of output optical fibers are arranged to receive the optical signal traveling through the free-space. In some embodiments, the output optical fibers are arranged along optical paths that are not co-linear with the first optical path. At least one substantially vertical, rotating micro-mirror assembly is located on the substrate in the free-space. The assembly includes a rotating micro-mirror with a vertical centerline and an axis of rotation both perpendicular to the surface, but not co-linear. The rotating micro-mirror is rotatable between a first position not in the first optical path and at least a second position in the first optical path. The rotating micro-mirror redirects the optical signal to one of the output optical fibers when in the second position.
The optical switch can include a plurality of input optical fibers. The input optical fibers are optionally arranged perpendicular to each of the output optical fibers. In one embodiment, the optical switch includes a plurality of output optical fibers generally arranged around the rotating micro-mirror assembly. In this embodiment, the second position of the micro-mirror comprises a plurality of positions each adapted to direct the optical signal to one of the output optical fibers.
In another embodiment, the optical switch includes a plurality of output optical fibers generally arranged perpendicular to the input optical fiber with a rotating micro-mirror assembly adjacent to the first optical path, but opposite each of the output optical fibers to selectively redirect the optical signal to any of the output optical fibers.
In yet another embodiment, the optical switch includes a plurality of input optical fibers each arranged to direct a discrete optical signal through the free-space. An array of rotating micro-mirror assemblies are constructed on the substrate and arranged to direct the discrete optical signals from any of the plurality of input optical fibers to any of the output optical fibers. The optical switch may optionally include a secondary array of output optical fibers arranged to receive the optical signals from one or more of the input optical fibers when the rotating micro-mirrors are in the first position. Each optical fiber in the secondary array is typically co-linear with one of the input optical fibers.
In one embodiment, the rotating micro-mirror rotates about 45 degrees between a first position and the second position. In another embodiment, the rotating micro-mirror rotates about 135 degrees between a first position and the second position.
In another embodiment, there is a gap between the axis of rotation and the rotating micro-mirror. The optical signal can pass through the gap without engaging the micro-mirror when the micro-mirror is in the first position. The rotating micro-mirror assembly may be mechanically coupled to a plurality of thermal actuators.
The present invention is also directed to an optical communication system including at least one optical switch in accordance with the present invention.